Enter the total rise. Get riser and tread sizes in inch fractions, the first-step cut that accounts for tread thickness, stringer length, a layout drawing, and a pass or fail against the 2021 IRC with the reason. Free, no account, runs in your browser.
Drop the first cut by the tread thickness. Every tread sits on top of the stringer, so a 1" tread adds 1" to the first step. If you cut the bottom of the stringer with a full riser, the first step comes out one tread thickness too tall, and every other step is correct. Code limits riser variation in a flight to 3/8", so a 1" error at the bottom fails inspection, and it is the step people trip on.
The fix is to cut the bottom plumb cut at riser minus tread thickness. This calculator does that for you and shows it in the drawing as the first cut. The top works the same way: the last seat is placed so the floor above lands at the full rise. If your top floor finish is a different thickness than your treads, adjust the top by the difference.
Numbers come from the 2021 International Residential Code, Chapter 3, R311.7, read on the ICC code site on October 30, 2026.
| Rule | Limit | Section |
|---|---|---|
| Riser height | 7 3/4" maximum. Largest riser in a flight within 3/8" of the smallest. | R311.7.5.1 |
| Tread depth | 10" minimum, nose to nose. Largest within 3/8" of the smallest. | R311.7.5.2 |
| Nosing | 3/4" to 1 1/4" projection. Not required when the tread is 11" or deeper. | R311.7.5.3 |
| Open risers | A 4" sphere must not pass where the drop below is more than 30". | R311.7.5.1 |
| Rise of one flight | 12' 7" maximum between floors or landings. | R311.7.3 |
| Headroom | 6' 8" minimum. | R311.7.2 |
| Width | 36" clear above the handrail. 31 1/2" with a rail on one side, 27" with rails on both, at and below handrail height. | R311.7.1 |
| Landing | At least as wide as the stair. 36" deep in the direction of travel on a straight run. | R311.7.6 |
Wood left under the notch (3 1/2" or more) is shop practice, not an IRC number. It is shown as a warning, not a failure.
Your local code governs. Jurisdictions adopt different editions and add amendments, so confirm with your building department. This page does not check stringer spacing or span, handrails and guards, winders, spiral stairs, or stairs outside the IRC. Treat the output as a layout aid, and test-fit a stringer before you cut all of them.
Yes, finished floor to finished floor, from the surface where the bottom step starts to the surface of the floor above. If the finish is not installed yet, add its thickness to the rise you measured.
Many tools report the diagonal of total rise and total run. The notch layout above has one fewer tread than risers and a first cut shortened by the tread thickness, so the board length here comes from the actual shape and the stock width you picked.
Enter your run available and leave the tread blank. The tread is sized to fit, rounded down to 1/16". If it falls below 10" you will see a failure, and the options are a landing, a different layout, or more room.
No. The calculation runs in your browser and nothing is uploaded or stored.